Wideband transistor amplifier



Feb. 26, 1963 T. POORTER 3,07

WIDEBAND TRANSISTOR AMPLIFIER I Filed May 16, 1960 AAAKAAAAA vvvvvvvvvv AAAAAAAAA Vvvvvvvvvv INVENTOR TEUNIS POORTER BY M e. AGENT United h 3,679,567 WIDIZEBAND TRAJSETGR AMPLEFEER Tennis Poor-tar, Eindhoven, Netherlands, assigncr to North American Philips (Zompany, l no, New York,

N.Y., a corporation of Delaware Filed May 16, 196i Ser. No. 29,322 Claims priority, application Germany Jane 4, 959 3 Ciaims. (iii. 330-21) The invention relates to a tnansistor amplifier for electric signals, in particular to an amplifier with a wide frequency range, for example for video-signals, in which the collector of a first transistor is connected to the supply via the series connection of a resistor and an inductance and the signals produced via this series arrangement are supplied to the base of a second transistor. The signals in the upper part of the frequency band are favoured by the self-inductance, so that the influence of internal cross capaci-tances, such as, for example, wiring capaoitances and natural capacitances of transistors respectively, can be compensated for.

The object of the present invention is to supply an amplifier with which a predetermined frequency characteristic can be achieved in a widest possible frequency range. A particular object is to supply a simple re-adjustmerit to compensate for the influence of the internal capacitances of a circuit element connected in the signal source, for example a camera tube. The amplifier according to the invention is characterized in that the resistor forms part of a potentiometer connected inseries with the self-inductance between supply and base of the second transistor, and the collector of the first transistor is connected to a variable tapping of this potentiometer.

In order that the invention may be readily carnied into efiect, it will now be describe in greater detail, by way of example, with reference to the accompanying drawing.

The FIGURE shows a signal source 1 which may cornprise, for example, a camera tube (vidicon) a succeeding amplifier, and which is followed by a transistor amplifier 2. The source 1 has a frequency characteristic which, at comparatively low frequencies, shows a real negative pole. In order to obtain a highest possible signalto-noise ratio, the camera tube is provided with an output resistor of the highest possible value forming this pole with the internal capacitances.

According to the invention, the collector of the transistor 2 is connected to a variable tapping 3 of a potent-iometer 4 which is connected in series with a self-inductonce '5 between supply and base of a second transistor amplifier 6. The capacitor 7 only operates as a separating capacitor and the resistor 8 serves to adjust the base bias current of the transistor 6. The amplified signals are derived from the output resistor 9.

The achievement of a wideband frequency characteristic, the two conjugate complex poles of which are substantially independent of the position of the variable tapping 3, is rendered possible by the series connection 4, together with the internal impedance of the input of the transistor 6. By displacing this tapping 3, the part of the frequency characteristic corresponding to these poles is not influenced. The upper part 4a of the potentiometer 4, however, together with the self-inductance 5,

3,91%,55? Patented Feb. 26, 1953 ice produces a real negative zero point by means of which the pole of the signal source 1 can be compensated for. By suitable choice of the above complex poles, a fiat tot-a1 frequency characteristic in a wide frequency range is obtainable which, when exchanging the camena tube, may be re-adjusted in a simple manner by adjusting the tapping 3. if by exchanging the camera tube, a change of the position of the pole of the supply 1 occurs in the supply 1, a corresponding change of the zero point of the series connection 4a5 is rendered possible by readjusting the tapping 3 or the potentiometer 4, without iniiuencing the fiat frequency characteristic which is ob tained by suitable proportioning of the series connection of the potentiometer 4 and the self-inductance 5 together with the input impedance of the transistor 6.

in a practical example, the following circuit elements were used: Transistors 2 and 6: 0C 171; resistors 4, 8, 9, it} and 11 of 30052, 4-7 K9, 15 KG, 209 and 1 K82; part of the resistor approximately 6052; self-inductance 5 of 4.5 ah; capacitors 7 and 12.- each of 50 t; supply voltage of 10 v.; the pole of the source 1 to be compensated for lay approximately at 2 mc./s., the band-Width of the total amplifier amounted to 10 mc./s.

What is claimed is:

l. A wide band transistor amplifier comprising first and second transistors, a source of signals, means applying said signals to the base of said first transistor, a source of operating potential, a series circuit comprising an indu-ctance, a resistor, and a capacitor serially connected in that order between said source of operating potential and the base of said second transistor, said resistor having a variable tap, and means connecting the collector of said first transistor to said variable tap.

2. A Wide band transistor amplifier comprising first and second transistors, a source of signals, a source of operating voltage having first md second terminals means applying said signals between the base of said first transistor and said first terminal, resistor means connecting the emitter of said first transistor to said first terminal, a series circuit comprising an inductor, a resistor and a capacitor connected in that order between said second terminal and the base of said second transistor, a variable tap on said resistor, means connecting said tap to the collector of aid first transistor, and means connected to said second erminal and tl e base of said second transistor to provide ase bias for said second transistor.

3. A wide band transistor amplifier comprising first and second transistors, a source of signals, means applying said signals to the base of said first transistor, 9. source of operating voltage, a series circuit of an inductor and resistor, the inductor end of said series circuit being connectes to said source of operating voltage, means connecting the resistor end of said series circuit to the base of said second transistor, said resistor having a variable tap, and means connecting said tap to the collector of said first transistor.

Ives et a1. Oct. 27, 1936 Braden Apr. 25, 1939 

1. A WIDE BAND TRANSISTOR AMPLIFIER COMPRISING FIRST AND SECOND TRANSISTORS, A SOURCE OF SIGNALS, MEANS APPLYING SAID SIGNALS TO THE BASE OF SAID FIRST TRANSISTOR, A SOURCE OF OPERATING POTENTIAL, A SERIES CIRCUIT COMPRISING AN INDUCTANCE, A RESISTOR, AND A CAPACITOR SERIALLY CONNECTED IN THAT ORDER BETWEEN SAID SOURCE OF OPERATING POTENTIAL AND THE BASE OF SAID SECOND TRANSISTOR, SAID RESISTOR HAVING A VARIABLE TAP, AND MEANS CONNECTING THE COLLECTOR OF SAID FIRST TRANSISTOR TO SAID VARIABLE TAP. 